If the drive wasn't selectable as a burning device then you're putting the DVD-R in the DVD-ROM drive, which can only read DVDs but not burn them. Besides, your DVD burner can only burn DVD+R media (no support for DVD-R), which indicates it's very old and probably won't be compatible with today's DVD+R media.
You should look into buying a new burner: they're pretty cheap nowadays and support both -R and +R formats. Also, unless you need the CD-ROM and DVD-ROM drives for some specific task, get rid of them as well